1. Field of the Invention
The present invention relates to a novel graft copolymer, a process for production thereof, and a plasticizer comprising said copolymer as the active component. More particularly, the present invention relates to a novel graft copolymer produced by graft-copolymerizing an alkylene oxide and a cyclic ester to a saponified ethylene-saturated carboxylic acid vinyl ester copolymer, a process for production thereof, and a plasticizer comprising said copolymer as the active component.
2. Description of the Prior Art
Many of synthetic resins and synthetic fibers are generally either hydrophobic or hydrophilic because of their molecular structures, and their applications have been developed by utilizing their properties.
Meanwhile, in recent years, the requirements for resins, etc. have been diversified and, in an increasing number of the application fields, resins, etc. alone have become unable to satisfy the requirements. Further, development of new materials has become necessary. In order to respond to the new situations, various measures have been taken.
These measures include, for example, (1) use of a compatibility improver in production of a resin of new properties (e.g. a polymer alloy) by mixing a plurality of resins, (2) use of an antistatic agent for suppressing the surface electrification of a resin and (3) use of a plasticizer of low evaporativity.
Saponified ethylene-saturated carboxylic acid vinyl ester copolymers, for example, a saponified ethylene-vinyl acetate copolymer are in practical use as an oxygen barrier resin, an adhesive for glass, an adhesive for padding cloth of fiber product, etc. by controlling the ethylene content, saponification degree, etc.
Also, graft copolymers produced by graft-copolymerizing an alkylene oxide to a saponified ethylene-saturated carboxylic acid vinyl ester copolymer are described in "KOBUNSHI RONBUNSYU" Vol. 36, No. 7, p. 489 (1979) and also in Japanese Patent Application Kokai (Laid-Open) No. 227307/1991. For example, a saponified product (hereinafter referred to as EVOH) of an ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) has nearly satisfactory compatibility with a polyolefin because it is a polymer and its main chain is composed mainly of a polymethylene structure.
A graft copolymer produced by graft-copolymerizing said EVOH with an alkylene oxide, for example, ethylene oxide has a property similar to that of ethylene glycol and is a highly hydrophilic resin.
EVOH, however, is not yet sufficient in compatibility with resins, has low plasticity, and is soluble in water when dipped therein, although it has a good antistatic property. Thus, EVOH is not fully satisfactory.